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Engine Coolant Temperature Sensors

Tiny
COPYCAR
  • MEMBER
  • 1995 MERCEDES BENZ SL600
  • V12
  • 2WD
  • AUTOMATIC
  • 72,000 MILES
The 1995 SL600 V-12 mercedes has 2 coolant temperature sensors with 4 pins that are not numbered. The new wiring harness has 2 plugs with 4 receptacles that are numbered 1 through 4. How do I know I am attaching the plug properly? There is no groove or deviation to ensure one way attachment of the plug.
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Thursday, March 3rd, 2011 AT 8:13 PM

21 Replies

Tiny
DOCFIXIT
  • MECHANIC
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Are you replacing ECTs? Or a wiring harhess? Is this a BOSCH part or after market?
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Thursday, March 3rd, 2011 AT 8:26 PM
Tiny
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I replaced the engine wiring harness with Mercedes dealer purchased harness and noticed that the new harness has the 2 numbered plug receptacles. The CTS in the engine are the original bosch products and the 4 pins are not numbered.
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Thursday, March 3rd, 2011 AT 8:32 PM
Tiny
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Mercedes does not provide complete wiring diagrams so have no way to trace wiring. Have you contacted dealer as to problem if harness was changed they would have directions or TSB. Can you match up old wiring colors to new and does color change at pigtail to ECT?
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Thursday, March 3rd, 2011 AT 8:38 PM
Tiny
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The new harness matches perfectly. The old harness plugs have the same numbered receptacles and I carefully marked the position of the old plugs with crayon before removal. I could make a determination of the pin position based on this marking but would rather have a definite answer.
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Thursday, March 3rd, 2011 AT 8:45 PM
Tiny
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You will have to get that from dealer
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Thursday, March 3rd, 2011 AT 8:47 PM
Tiny
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The mechanic at the dealer claims he does not know. I would think if it mattered that there would be a groove or deviation in the CTS that would allow only one way of connecting the plug. Perhaps it does not matter?
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Thursday, March 3rd, 2011 AT 8:51 PM
Tiny
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I would go with pin position it will not harm if it is wrong. May get a engine light
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Thursday, March 3rd, 2011 AT 9:00 PM
Tiny
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I will try that and if it runs rough while cold I can shut down and reposition each plug clockwise one pin until it smooths out.
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Thursday, March 3rd, 2011 AT 9:08 PM
Tiny
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Great idea let me know what happens
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Friday, March 4th, 2011 AT 3:37 PM
Tiny
COPYCAR
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I discovered that the pins diagonally from each other complete the circuit and operate the same valves. Therefore it does not matter which way the plug is attached.

I completed the installation of the engine wiring harness and now the engine will not start.
Do I have to clear the computer before it will start?
The car was running when I drove it into the shop to replace the engine wiring harness. The old harness was completely falling apart with some of the wiring completely bare of insulation and the engine still ran.
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Monday, March 7th, 2011 AT 12:33 PM
Tiny
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Well guess something went wrong does engine crank? Is there spark at plugs? Fuel to injectors?
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Monday, March 7th, 2011 AT 2:24 PM
Tiny
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The engine cranks. I'll check to see if the plugs fire. How do I check on fuel delivery?
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Monday, March 7th, 2011 AT 2:34 PM
Tiny
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On fuel rail for injectors fine service valve key on depress fuel should spray out
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Monday, March 7th, 2011 AT 7:36 PM
Tiny
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I will do that and will also check the spark plugs to see if they are firing. Where might I locate the LH control Relay? Does this engine have cold start injector(s)?
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Monday, March 7th, 2011 AT 7:40 PM
Tiny
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No cold start what is LH relay?
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Monday, March 7th, 2011 AT 7:49 PM
Tiny
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I think it controls the power supply for the fuel injectors. It is short hand for the German words, Luftmassenmesser Hitzdraht and is common on pulsed injection systems. I am new to this level of technology and am reading everything I can get my hands on to solve this piece of the puzzle.
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Monday, March 7th, 2011 AT 7:57 PM
Tiny
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Don't speak German only thing found with LH is a control module
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Monday, March 7th, 2011 AT 8:06 PM
Tiny
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LH translates to air flow meter.
Would these illustrated in the diagram be in the same location on the 129 chassis?
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Monday, March 7th, 2011 AT 8:11 PM
Tiny
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That would be what air snorkle attaches to. Fuel system has electronic controled injection right?
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Monday, March 7th, 2011 AT 8:24 PM
Tiny
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Yes it has electronic controled injection. Where is the air snorkle?
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Monday, March 7th, 2011 AT 8:36 PM

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